As network technologies such as the Internet have been advanced, content data such as music data and picture data have been freely distributed. As a result, copyright protection technologies have become increasingly important. As one of the copyright protecting technologies, a watermark technology for embedding copyright information in content data is known. Although a watermark has a function for embedding copyright information in content data such as music data, picture data, and so forth, it is difficult to distinguish music data, picture data, and so forth in which a watermark has been embedded from those in which no watermark has been embedded. Using dedicated hardware or software, copyright information concealed in content data can be detected.
However, conventionally, it was assumed that a watermark could be transmitted as both an analog signal and a digital signal without any problem. To prevent a watermark from affecting visual and auditory senses of data as a content and from being lost during the transmission thereof while satisfying such a condition, the strength of the watermark should be improved. To do that, the embedding process and the detecting process for the watermark become complicated.